My next hexapod project, codename BMX

Hi,

I hope you all are having a nice Christmas!

For a long time I've been thinking about some new projects to work on. Since 2006 I've made a few more and some less successful robots, mostly hexapods but also an octopod, a biped and a quad. For me this hobby has been incredible fun and I've learned a lot from people like Kurt Eckhardt and Jeroen Janssen. Until now all my custom made robots has been RC servo based, mostly using the popular SSC-32 servo controller combined with the Basic Atom Pro 28 (BAP28) mcu.

I think I was pushing the limits (payload capacity and complexity) when using RC-servos on my last project MorpHex. Using some sort of serial bus controlled servos would certainly make the wire work a lot easier.

From now on I've decided to go dark.. Lately I've invested in several MX-106T and MX-64T servos.

At first I'm going to make a rather simple 3 DOF hexapod. I'm thinking more "Back to the basics". I want a good platform for experimenting on new code, terrain adaptation and learning new stuff, especially C++ and the Teensy.. My plan is to make a rather light weight hexapod with large leg segments and a relative small body. Since the cost is so high I'll probably reuse the servos for several future projects.

When I'm done with the hardware I'll study what others like KevinO and KurtE has done. I probably need to pick up some books about kinematics again.

Until now I've not used any form of CAD when designing my robots. So I'm a total noob when it comes to that part. So far I've peeked at almost every free CAD solutions. At first I ended up with Autodesk 123D, but I find it a bit limiting and a bit frustrating to work on. I've also tried freeCAD but found it a bit overwhelming at first, but I might give it a second try. Any other suggestions for a good low cost CAD solution is appreciated.

Like I said I'm going for a simple design at first. I decided to go for the MX-106T for both femur and tibia. The MX-106T has a much better weight/torque ratio than the MX-64T. For only 26 gram additional weight (158 gram vs. 132 gram) you get a lot by upgrading from the 64's to the 106's. Here is a picture of how I plan to design the leg:

The femur are going to be made of 4,76mm Delrin and the length is 18cm (servo center to servo center) and the tibia (3,15mm Delrin) is about 27cm (servo center to tars/foot). I've not completely designed the tars (foot) section yet. But it will be relative simple at first, I'll later replace it with a foot with sensors/switches. A while ago Tyberius (Andrew) was very kind to laser cut some test parts for me so that I could get the feeling of the Delrin plastic. My first attempt on the femur got very solid and rather heavy. After the test I removed more material and made it slightly slimmer. A Picture of my first attempt:

My progress is very slow, due to life.. Little free time. But today I'm home alone, lol. Giving me time to finally make a post on the forum and making a simple and relative small body for the hexapod. I'm not finished with the body section yet. I'll probably add a smaller top section for covering electronics. The 5000 mAh 3S LiPo takes most of the space inside the body.

Some pics of the hexapod:

In this picture I've just lifted the battery for illustrating the battery size vs body size:

Again, I find Autodesk 123D terrible to work with when the model gets more complex.
My plan is to bend the tibia sections slightly closer at the foot section. I've no idea how to bend them in Autodesk 123D though, lol.

Re: My next hexapod project, codename BMX

Can't wait to see the evolution of your project. You will get spoiled with the MX-64's and MX-106's. I thought the AX's were great but I was amazed with the MX line once I switched. You might want to try a lower deck for the battery. On my 64 hex I had the battery and the hubs on the lower deck so I could easily get to them without bothering the other electronics.

Re: My next hexapod project, codename BMX

Hi again Kåre,

Glad to see you on the Dark side :lol: I too have lost interest in doing anything these days with RC servos and SSC-32 and will probably sell off a few of my Lynxmotion based robots... Sorry I don't want to pollute your thread.

I can not wait to see what you come up with, both Hardware wise but software wise as well.

Personally on the electronics side, I am not sure what I would suggest. As you know I really like the Teensy 3.1 and you have one of my breakout boards. It is great to see that Trossen now sell them (http://www.trossenrobotics.com/teensy-3-1) This is a great little platform, which I will continue to use. You can probably do most everything you need with this platform. This will be especially be true when he comes out with the more powerful version.

My PhantomX currently has the Arduino version of the Edison with XBee and 2.8" TFT shield and USB2AX to control servos. Over the next couple of days, I will post more on this on a different thread. (Playing with control console app for TFT display). Then I am thinking of maybe switching out the USB2AX to a Teensy, which I believe will be closer hardware wise to what Trossen will be doing (Arbotix Pro?). Not sure when I do that if I will also move Display to this one as well? Who knows maybe need to design new version of Teensy board specific to this. Or may try Arbotix Pro once I can get my hands on one and know more about it.

If you (or someone else) wish to give Edison a try, not sure which way suggest to do this. That is, I have a version or two of the Phoenix code bases running on the Edison, through different means.

The first way is using the Intel Arduino IDE. I have a version that works with the Arduino breakout board. It may also work on Mini-breakout. Problem is that Intel has only setup an Arduino board variant for the Arduino board. I have a version that I am playing with, with pin definitions for the mini...

Then their is doing the stuff completely native using the linux setup on the board. Gives you complete control, but a pretty big learning curve. Again have version for this (My Raspberry Pi project). Some day this will probably be converted to ROS and cmake files...

Currently I am doing stuff using the Eclipse IDE with the Intel stuff including cross compilers. You are still programming for the native Linux system, but you are doing all of your editing and the like directly on your PC (Windows, Mac, Linux). I am still adapting for the Eclipse IDE as I am used to others, so I am still trying to get automatic on what is the key stroke for find next... But, the IDE does a lot of nice things for you, like it scans the sources and knows what the members are of a class, so it detects if you do something wrong, can paste in function prototypes... But the most fun and useful thing, is it is setup to download your programs to the Edison using wifi, and you also have the ability to do Source level debugging again over wifi. This has probably a little bigger learning curve than using the Arduino IDE and Intel's documentation on how to do things is not the greatest, but if you (or anyone) is interested I will be uploading my Eclipse workspace for the PhantomX to github at some point.

Again sorry if the above is a little off topic. If you are interested, can continue this in different thread, or PM or...

Re: My next hexapod project, codename BMX

That looks like a great project!

From Onyx, I learned that the femur probably doesn't need the cross braces (which add weight) because it's tight in both ends against the servos. The tars, however, needs some cross brace to fix the foot -- the blue pictures you have make me fear that the feet will bend the tibias out of true.

Another option to consider for controllers is the OpenCM-9.04. It's $10 ($15 if you don't have the connectors to solder in in the parts bin alread, $20 if you don't want to solder yourself) and it comes with libraries from Robotis to read/write the Dynamixels. I find the software stack to be slightly more robust for the Teensy, but the integration specifically with the TTL bus to be better on the OpenCM.

Re: My next hexapod project, codename BMX

Thanks for your input guys!

I think I'll stick to Teensy at first and at a later stage move over to a more sophisticated platform(s)..
FP would certainly help though. Kurt, are you planning to make a new board for that, when it is available?

So far I think I'll try to fit the battery and electronics inside the body. By rotating the battery 90 degree there is much more extra space for the rest.

I've been playing with different ideas for the upper body plate. Using CAD really help visualizing.

Another approach using a top deck. I've not added any spacers, just for visualizing.

Re: My next hexapod project, codename BMX

Originally Posted by jwatte

That looks like a great project!

From Onyx, I learned that the femur probably doesn't need the cross braces (which add weight) because it's tight in both ends against the servos. The tars, however, needs some cross brace to fix the foot -- the blue pictures you have make me fear that the feet will bend the tibias out of true.

Thanks for your input Jwatte! I didn't see your post until after I had submitted my last post.
I do plan to make some holes for cross spacers on the tibias. From what I've experienced the extra support on the femur wouldn't hurt since the sections are rather long.

The tars section on the tibia isn't finished. At first the foot/tars will look something like this (upside down):

Re: My next hexapod project, codename BMX

That looks like a well designed foot knob!

If you bend the tibias, won't they rub against the servo body in certain angles? Or are they flush to the servo flanges, and bend below/after that?

Btw: If you're really into CAD, I highly recommend Autodesk Inventor. It costs a fair bit if you buy it for professional use, but there may be other ways of getting it legally for hobby use, including:
- If you have a Tech Shop membership, they can install a 6 month copy for you, and you can refresh this eery 6 months.
- There is a 30 day free trial. Depending on your appetite for installing on fresh virtual machines, and creating new email accounts on autodesk.com, this can last you a long time. As long as you don't sell anything made this way, it's probably not on the dark side, maybe. (This is not legal advice)
- If you are writing a book, you may qualify for the author discount for ADN (their developer support.) I think this is a few hundred a year, and it includes almost all versions of almost all Autodesk software (3ds Max, Maya, Inventor, Mudbox, ...) You will be expected to actually publish something at some point, I think :-) These are non-commercial installs -- not for use for commercial work.
- If you are a developer, you can buy a single-seat ADN license, which has the same benefits as author's license. This is a yearly cost, but may be cheaper than the full price. Again, these are non-commercial copies, made available so that you can build plugins and integrate with Autodesk software. (They do accept plug-ins for internal-only tools, I think, so there's probably no publishing requirement here.)

I'm a TechShop member, AND we have a 5-seat ADN subscription at work because we ship 3ds Max exporters for our art path, so I have two ways into that path. Others may have to look at the other options. Even if you mainly just use the solid construction and drawing tools, Inventor works better than the free/share/cheap-ware I've tried. All the FEM simulation/structural and materials stuff is wasted on me :-)